Chucks, such as pin chucks, are used to hold flat components for processing. The most common use is to hold wafers (Si, SiC, GaAs, GaN, Sapphire, other) during processing to yield a semiconductor device. Other uses include holding substrates during the fabrication of flat panel displays, solar cells and other such manufactured products. These chucking components are known by many names, including wafer chucks, wafer tables, wafer handling devices, etc.
The use of pins on these devices is to provide minimum chuck-to-substrate contact. Minimum contact reduces contamination and enhances the ability to maintain high flatness. The pin tops need to have low wear in use to maximize life and precision. The pin tops also need to be low friction so the substrate easily slides on and off, and lies flat on the pins.
A pin chuck consists of a rigid body with a plurality of pins on the surface on which the substrate to be processed (e.g., Si wafer) rests. The pins exist in many geometries, and go by many names including burls, mesas, bumps, proud lands, proud rings, etc.
Regardless of whether the chuck is of the “pin” type or not, the surface that supports whatever is to be chucked (e.g., a semiconductor wafer) needs to be flat to a very high degree of precision. In the case of semiconductor lithography, the flatness is measured in nanometers (nm).
Machines exist, for example, those used in a “deterministic” fashion, to locally correct errors in flatness (surface elevation). Some techniques for this deterministic correction include, but not limited to, Ion Beam Figuring (IBF), Magneto Rheological Finishing (MRF), and computer controlled polishing (CCP). As used herein, the phrase “deterministic correction” means that figure, elevation or roughness data as measured for example, by an interferometer or profilometer, is fed into a finishing machine such as a lapping machine. The input may consist of one or more algorithms for optimizations such as convolution or transforms to optimize the tool path or footprint in such a manner that the machine most rapidly converges to the desired target shape with a minimal amount of time, cost or risk. It effectively treats those areas of the work piece that are in error and need processing (e.g., grinding, lapping or texturing), while minimizing the effort spent working on areas that are not in need or alteration. The machine does not automatically treat the entire surface of the work piece.
The instant invention is not limited to machines that operate deterministically, but it will focus on those that employ physical contact of a tool here termed a “treatment tool” with the surface of a work piece to be processed to physically remove material from the work piece through grinding, lapping, texturing and/or polishing.
FIG. 1 illustrates an example of a prior art machine. The work piece is mounted on a shaft “theta” that rotates, while treatment tool is mounted on a fixture that can move radially R with respect to the theta rotating axis. Thus, there are here two degrees of freedom of the treatment tool relative to the work piece: radius, denoted by “R”, and rotation of the work piece, denoted by “theta”.
One problem with this “R-theta” arrangement is that the treatment tool cannot process regions on the work piece that are very close to, or at, the center of the theta axis.
The machine of the instant invention addresses this problem, and provides a solution.